The basic principle of these lamps is the generation and emission of radiation by means of a dielectric barrier discharge. Usually, at least one of the two electrodes of such a lamp is located outside the discharge volume. The discharge volume comprises a discharge gas, especially at or around the lamp envelope, wherein the energy supply is accomplished by capacitive coupling through the walls of the lamp envelope into the discharge volume, in order to initiate within this volume the gas discharge and the excitation and emission of radiation.
Typically, these lamps have a cylindrical, a dome shaped or a coaxial construction and they are cooled by means of an internal and/or an external flow of water. In case of a coaxial design the lamp usually comprises an inner and an outer quartz tube which both are coaxially arranged to each other and are melted together at both their axial ends so that an annular discharge volume is delimited between both.
Generally, such dielectric barrier discharge lamps are used as an alternative to conventional mercury based discharge lamps in a wide area of applications, where a radiation of a certain wavelength has to be generated for a variety of purposes. Some applications are for example the generation of ultraviolet (UV) radiation with wavelengths oaf between about 170 nm and about 380 nm for industrial purposes such as waste water treatment, disinfection of gases and fluids, especially of drinking water, dechlorination or production of ultra pure water, activation and cleaning of surfaces, curing of lacquers, inks or paints, ozone generation, or for liquid crystal display (LCD) backlighting or photocopiers and others.
Furthermore, dielectric barrier discharge lamps are of increasing importance especially as a source for generating and/or emitting high intensity and high power ultraviolet (UV) radiation in a narrow and well defined spectral range with high efficiency and high radiation intensity.
WO 2006/006139 discloses a dielectric barrier discharge lamp comprising a discharge gap being at least partly formed and/or surrounded by at least an inner wall and an outer wall, wherein at least one of the walls is a dielectric wall and at least one of the walls has an at least partly transparent part, a filling located inside the discharge gap, at least a first electrical contacting means for contacting the outer wall and a second electrical contacting means for contacting the inner wall, and at least one multifunctional means which is arranged adjacent to the discharge gap and which on the one hand serves as an improved and optimized ignition aid, especially for initial ignition or ignition after a long pause, and on the other hand serves at least as guiding means for easily arranging two walls towards each other, thereby forming an optimized discharge gap especially for coaxial dielectric barrier discharge lamps.